ML19221A615

Task 15:Evaluation of Pros & Cons of Alternate RHR Sys & Provide Recommendations

ML19221A615
Person / Time
Site:	Crane
Issue date:	04/15/1979
From:	Lichtenberger INDUSTRY ADVISORY GROUP
To:
References
OSP-790415, TASK 15, TASK-15, NUDOCS 7905230438
Download: ML19221A615 (8)

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/ INTRODUCTION h

Problem Statement - Evaluate the pros"and cons of the alternate RHR system and provide recournendations.

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Sumary of Action - The above p oblem was presented to the Industry' Advisory Group which has made a brief investigation, sur:::arized the perceived risks and advantages in regard to the various alternates and developed a set of recomendations.

RECONENDATIONS The reccanendations of the group are as follows:

1.

Upgrade the present RHR systems to improve their reliability for long term operation under high radiation and minimum maintenance conditions. Make only those changes which are considered to be absolutely necessary.

Some' -

suggested areas are:

- revise the pump motor lubricating system to function with the expected radiation exposure;

- remove the strainers fran the pump suct!on pipes if this has not already been done;

- add remote instrumentation where such will be helpful in understanding system coditions (also consider relocating present instrunentation to I

minimize personnel exposures);

- add drip catchers, dikes, or other means to minimize problems due to lea.:s;

- add shielding in strategic locations to permit access with tolerable personnel exposures.

2.

Arrange to have B&W engineers participate in the improvement program for the present RHR systems and the design of the new skid mounted RHR system.

3.

Seview all available data ~on operation of other RHR systems of the same design to identify problems and corrective actions taken.

4.

Continue the design and construction of. the skid mounted system including the excavation and other site work necessary to allow penetration of the auxiliary building wall.

5.

We favor the addition of the new pipe connections to the existing RHR frcn the inside of the auxiliary building without breaching the wall if practical.

Thus, providing that levels of exposure allow, we recur 4 installation of the tAes and valves in the three RHR lines and stub off inside the building uall in such a location as to allow connection at a later date when the building wall would be penetrated from the outside.

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. r AE HENDATIONS (CONT.)

Page 2 6.

If this is not prac~tical, then build a valve pit outr'de of and against the auxiliary building of sufficient size to allow working space for cutting through the building wall and making up the piping. The valve pit should be essentially an extension of the auxiliary building and should meet all the design requirements of that building for handling and containing radioactive materials and for protectica against external loadings; e.g., seismic, plane crash, etc. Once this valve pit is completed and sealed off, cut through the auxiliary building wall and install the pipe connections and valves.

7. ' Start now on a permanent building including planning for clean-up of the water systems and decontamination bf the buildings. This building should have all the features necessary to the operation of radioactive material handling systems.

The location selected for the skid mounted RHR system sppears to be the best site for this permanent building. There should be" no temporary building as currently planned.

It's design should be revised to be permanent as described here.

8.

Notwithstanding any of the above, the existing RHR systems availability should be maintained and, should the necessity arisa, use th* present systems. Once the new RHR system is installed in a structure equivalent

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to the present auxiliary building, use this new system in preference to the present systems. We strongly reccmend against hooking up and operating the alternate RHR system without these provisions, unless it is deemed as absolutely necessary.

ALTERNATE RHR RISKS AND ADVANTAGES The proposed alternate RHR (Reactor Heat Removal) system design was reviewed I

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to identify potential risks and advantages which should be considered prior to I

breaching the reactor auxiliary building wall to make the final hook-up. The I

primary risks identified in order of decreasing importance are as follows:

1.

The new system, as currently planned, will bring primary coolant outside the primary containment and auxiliary building and into a te-:porary housing of questionable integrity.

2.

There is a high potential for impact on -the on-going recovt.ry program on the island due to radiation leakaga to the local surroundings unless the temporary RHR building can be well-shielded and have provision for tight leakage control.

3.

Cutting into and opening the auxiliary building, as currently planned, basically involves penetration of an important boundary to radiatica release for the duration of the cut and repair, unless a pernanent concrete structure with leak tightness, equal structural integrity tdthe auxiliary building and external access provision is first constructed 'Arcund the intended location for the cut.

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ALTERNATE RHR RISKS AND ADVANTAGES (CONT.)

Page 3 The secondary risks id'entified in order of decreasing importance are as follows:

4.

Cutting into the existing RHR syste.n suction pipe will re:nove both the existing RHR systeas from servics for the duration of the cut and closure, and will also run the risk of high dose due to possible suction line iso!ation valve leakage. The dosage risk also exists as each discharge line is cut into.

However, since these cuts and closures would be made one line at a time there would always be at least one RHR system available for service if needed.

5.*'There would be a high isk of increased contamination of portions of the existing ilHR system, i.e. discharge piping downstream of the RHR heat exchangers, and suction pipirig upstream of the RHR pugs, if the new alternate RHR system were used first, instead of using the existing RHR.

6.

There is some risk that the very accelerated schedule for completing the design, fabrication and testing of the new system, introduces increased potential for design or operational problems resulting from error, as well as possible shortcuts on acceptance criteria.

The primary advantages identified in order of decreasing importance are as follows:

1.

As currently planned, the addition of the alternate RHR, brings a new piping connection point to the primary system outside of the high radiatica This connection point can be used for possible future primary coo], ant area.

system additions or improvements that may be deemed necessary.

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2.

The addition of an alternate RHR provides one more backup cooling system I

that could be used if needed.

3.

The alternate RHR system, as currently configured, has a rainimum number of valves and better instrumentation for monitoring system performance than the existing system.

This should minimize the potential operational problems.

4.

The alternate R*!R system, as cu.-ren'.iy configured, is outside the auxiliary building and would thus be more an.ssible for routine maintenance and surveillance.

DISCUSS 10fi 0F RISKS AND ADVANTAGES h

Ps icary Risks (i

We view as the major concern the risks associated with bringing the prizary coolant outside both the contattrent and the auxiliary buildingitato the proposed tenporary trw.ing, " quonset hut."

The proposed structure is of W esticnable integrity both frem a radiation leakage concern and from ability to withstand unexpected (yet possible) external loadings; e.g., plane crash, truck or other

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site equipment. Bringing the high activity primary coolant into such a 11 igg f

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A ry Ri g (Cont.)

Page 4 tside the contain.nent definitely reduces the barrier to fission product

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effectiveness of the overall system in containing the activity.

In our view, this is the most important risk associated with the current plan.

A corallary to this primary risk is that operation of the alternate system in tiie temporary housing will significantly increase the risk of exposing site j

workers to unacceptably high radiation doses.

This risk would likely result in some impact on the on-going site recovery activity on the island; 1.e.,-

8 it adds additional risk and restriction to an already highly constrained I

activity. This risk is considered to be a close second in importance relativt the primary risk above.

The third risk identified, as with the second, ranks high in importance. Cutting into and opening the auxiliary building for the duration of the work breaches the final outermost barrier fer external radiation release, abeit for a short'-

while. Unless a permanent structure of equivalent integrity; e.g., structural, leak-tightness, and external access provision, is first built around the intended cut in the auxiliary building wall and sealed off, prior to the cut there is a very undesirable reduction in the barrier to activity release.

Secondary Risks The next most significant risk identified is that there will be a time period when both existing RHR systems will be unavailable fdr any service while the decay heat suction line is being cut into and then the new piping closure is

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.d e. There is also a radiation exposure risk associated with this operation

s Tor both suction and discharge pipe cuts and reclosures, which is particularTy-r uncertain because of the unknown leakage via the existing isolation valves.

This risk is considered secondary to the first three identified and is,not of p

sufficient concern to argue against adding the new piping connection.

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it is a risk which can affect the schedule and progress of this activity.

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There is an additional risk of increased contamination of portions of the existing RHR system; i.e., disc,harge piping downstream of the RHR heat exchagers, and suction piping upstream of the RHR pumps, if the alternate RHR system were used first.

This is a secondary risk, but should be kept in mind since one of the reasons for going to an alternate RHR system was to apparently keep from crapping up the existing RHR and auxiliary building if at all possible for future availability during clean-up operations.

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The final risk identified was that the accelerated schedule for design and h

fabrication introduces opportunity for future design and operational problems due to errors and/or shortcuts on acceptance criteria. Actually, although y-this risk exists, it appears that precautions are being taken to assure that h*

errors are avoided and that all normal design and licensing criteria are 4-sa tisfied. There appears to be significant review by Westinghouse and the

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NRC, ncrmal qt.ality assurance requirecents are being epplied andJndustry

,,J code criteria and documentation requirer.:ents are being followedy).s

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_econdary Risks (Cont.)

Page 5 30

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One important additional action which should, however, be taken is to ~ involve B&W engineers early in the design review process for the alternate system as well as for the design of any improvements planned for the existing RJiR systent. T [ '

s s.av Advan tages In our review, the rost important ad' antage of the planned addition of an alternate RHR is that it creates a ni e piping connector point to the primary system outside of the high radiation.

This connection point, whether it is used at this time or not, provides the flexibility for nwnerous possible future actions that may be desired; i.e.. decontamination provision, methods for improved core cooling, etc. This. may prove very useful and is a good insurance policy against potential future problems with operation in the cooled-down mode.

The obvious additional advantage is that one more alternate backup cooling system would be available if ever needed. While it is not currently intended for use unless necessary, if it were provided in an adequately designed structure, it would provide additional assurance of long-term safety.

There apoears also to be an advantage to the altermate system in that it is designed to perform only one function, and as : consequence, has a minimum of unncessary frills; e.g., a minimum number of valves.

Also, the al ternate system appears to have more complete instrumntation for monitoring operational performance.

The final advantage identified in this review is that the alternate RHR system.

as currently configured outside the auxiliary building, would be more accessible 1

for routine maintenance and surveillance.

Thi s is an obvious advar'. age which j

would make it more desirable as 3 long-term cooling system if one wera needed.

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April 17, 1979 H. Lichtenberger Addendum to the Industrial Advisory Grcup report on Task 15 - Evaluate the pros and cons of the alternato RHR system and provide reco=mendations.

In an effort to further clarify the recc==endations of the Industrial Advisory Group in regard to the alternate RHR system, a discussion was held with the Westinghouse design group on the afternoon of April 16, 1979 and the following generally agreed to:

1.

Priority second only to upgrading of the present RHR system should be given to making the connections ;o the present lines, installing the valves and bringing the extensions to the building wall in position for later hook-up from outside.

2.

The general scheme as proposed by Westinghouse for support of the piping and shielding by the use of a canned penetration fastened to the building wall appears to suit the requirements.

,4 3.

In order to decreast the tice required when the final connection is being made, a cut three-quarters of the way through the wall could be made now.

4.

The valve compart=ent to be constructed outside the building should be a permanent structure designed to suitable high integrity requirements so as to reduce the probability of release of radioactive materials to the practical minimum.

Effort should be concentrated on the permanent facility.

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location of this structure needs to be taken into account in locatir g...

N the " temporary" RHR system.

Provision should be made to allow for p

expansion of this building and for the addition of further systems for 3

plant clean up.

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The "te=porary" system should meet the following requirements:

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- Shielding should be adequate to permit normal operations in adjacent areas without undue personnel exposures.

This could be encrete blocks, precast slabs. or some combination of these with her materials.

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- The building should be sealed and provided with forced ventilation with shut-offs and filtration.

- Provisions should be made to control fluid leakage.

Drip pans, sump pumps and return lines to the system or to the auxiliary 1;uilding should be considered.

7.

In view of the Ice probability for a seismic event or impact by aircraft during the proposed short term use of the system, consideration

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of these and similar unlikely possibilities need not be factored into the design.

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